Mineral admixtures and chemical admixtures are the extra ingredients other than water, cement, aggregates and fibers. These are added to the concrete batch plant during batch mixing or at the start when other quantities are added. Admixtures offer very favorable effects to the properties of fresh or hardened concrete only if proper use of admixtures is made possible.
Admixtures improve the quality of concrete, accelerate setting time, and decelerate setting time in case of any misshaping. Now there is a wide range of admixtures available in the market that enhanced resistance against freeze and thaw effect. It made possible of earlier attainment of strength.
Admixtures enhanced the workability of fresh concrete with lesser amount of water than the required one. In this case concrete will have more strength, because water aids in workability but in the same manner it has a negative effect on the strength of concrete. Therefore, finish-ability of concrete also becomes noticeable.
Types Of Admixtures
Chemical composition of admixtures has a very wide range. Depending upon the functions and composition, admixtures are mainly divided in to two main types. These are;
- Mineral admixtures (finely ground solid material)
- Chemical admixtures (water soluble compounds)
Mineral admixtures are the fine ground solid materials I.e. Fly ash, slag and silica fume. It is added to the concrete generally in larger amount than any other type. Because mineral admixtures have an ability to enhance workability as well as finish-ability of freshly laid concrete. Mineral admixtures are also utilized as a replacement of cement. As cement is the most expensive material in concrete. Hence, with the use of mineral admixtures reducing concrete cost is very likely possible.
Mineral admixtures are the waste products of industries. Hence by using in concrete, maximum sustainability can be achieved. It also supports in reducing thermal cracking in concrete by reducing heat of hydration. At the end we can say that this type of admixtures enhances the durability and serviceability of concrete.
Chemical admixtures are the admixtures that are added to concrete in a very small amount for a specific function to concrete. If chemical admixtures are added more than the defined than it has a very wide range of negative effects on the properties of fresh as well as hardened concrete. Chemical admixtures are more likely to be added as a water reducing admixtures, as a retarding setting time, accelerating setting time, as a super plasticizer or added as an air-entrainment.